file1.php
<?php
$a="hello I'm file1";
echo $a;
?>

file2.php
<?php
$a="hello I'm file2";
include ('file1.php');
echo $a;
?>

when I call file2.php, what I want is to have 
hello I'm file1
hello I'm file2

and not
hello I'm file1
hello I'm file1